Thus, document U.S. Pat. No. 1,273,287 forms part of the technological background and not part of the technical field of the invention. That document describes a cable cutter suitable for being arranged on a bayonet and making use only of a pivoting knife in order to cut through said cables.
Cables, such as telephone cables or high-voltage electricity cables, constitute a significant danger for helicopters.
Because of the kinds of mission that they perform, helicopters fly at low altitude and run the risk at any time of coming into collision with a cable. Even if the pilot of the helicopter pays particular attention, it remains difficult to see a cable having a diameter of 1 centimeter (cm) or 2 cm, for example.
In forward flight, the helicopter thus runs the risk of striking a cable. Under such circumstances, the cable slides along the cockpit and then comes into contact with the rotor mast or else with the landing gear, and that can lead to a catastrophic situation.
It should be observed that most accidents that occur during low-altitude flights result from a helicopter colliding with a suspended cable.
Helicopter manufacturers have thus implemented devices suitable for cutting a cable while in flight in order to protect their helicopters in the event of an accident.
Document U.S. Pat. No. 4,407,467 describes a first device provided with a structure at the front of the helicopter, said structure supporting a plurality of explosive charges.
When the helicopter strikes a cable, the cable slides along the structure until it reaches an explosive charge that explodes on coming into contact therewith, thereby cutting through the cable.
That first device fulfils requirements; however it can be dangerous, since metal elements might damage the helicopter at the time of the explosion.
In addition, the carrier structure is found to be heavy, bulky, and not very aerodynamic.
Document WO 2006/068507 discloses a second device for cutting cables.
That second device recommends using pairs of electrodes mounted on the fuselage to cut through a cable, if any.
That second device differs completely from the first device, but it requires a constricting electrical installation.
Furthermore, that second device tends to present risks for personnel on the ground close to the aircraft.
Document U.S. Pat. No. 4,826,103 discloses a third device.
That third device includes a jaw provided with a top portion and a bottom portion that define a notch. That third device is also provided with a knife that is set into movement by an explosive charge to cut through a cable in the notch.
The presence of an explosive makes using that third device difficult or even dangerous, and also requires maintenance that is relatively constraining.
Finally, document FR 2 443 309 discloses a fourth device for cutting a cable under mechanical tension, said device comprising a pair of stationary sharp edges that co-operate with each other.
Those two sharp edges are then arranged in such a manner as to form an angle between them that produces a sloping plane effect or wedge effect while also presenting a cutting face to a cable that comes into contact with said sharp edges.
That fourth device is very effective for cables of medium diameter, of the order of 11 millimeters (mm), and/or suitable for withstanding a maximum force of about 80,000 newtons (N).
Similarly, that fourth device is effective at low speeds, lying in the range 20 kilometers per hour (km/h) to 120 km/h, but it is of limited effectiveness at faster or slower speeds that lie outside said range.